1. Field of the Invention
The invention is directed to an improved piston pump of the type used in particular in hydraulic units of hydraulically controllable brake systems in vehicles and is used to produce the required pressure for modulating brake pressures in the different wheel brake cylinders.
2. Description of the Prior Art
A piston pump of the type with which this invention is concerned is already known, for example, from DE 199 28 913 A1 which is comprised, among other things, of a pump housing that contains a pump bore into which a bushing is inserted. The bushing axially guides a pump piston that can be driven into a reciprocating stroke motion. To that end, the piston cooperates with a rotating cam and a return element in the form of a compression spring. This known piston pump is supplied with pressure fluid via a pressure fluid inlet and a pressure fluid outlet, which are respectively connected to inlet and outlet conduits for the pressure fluid in the pump housing. In order to damp pressure pulsations that are generated by the working principle of the piston pump, a throttle is provided in the outlet conduit that drains away the pressure fluid. This outlet conduit is provided on the inside of a sealing piece, which seals the pump bore off from the environment. No filter is provided to protect the throttle from becoming clogged by impurities in the pressure fluid. The outlet conduit extends along the end surface of the bushing and feeds directly into a pressure fluid conduit leading radially away from the piston pump.
Based on this prior art, the object of the invention is to provide a design that makes it possible to inexpensively provide a filter and a throttle while simultaneously not requiring much space, and also offers the possibility of connecting an additional damping element in parallel with the filter in order to further improve the damping properties. This object is attained in an embodiment in which at least part of the pressure fluid outlet is routed along the circumference surface of the bushing and in that in the region of this section routed along the circumference surface, a filter and a throttle are provided, which are of one piece with the bushing.